Pettuleipä

Bark bread is a traditional food made with cambium flour. It has a history of use as famine food. Bark bread seems to be a primarily Scandinavian tradition. Bark bread is mentioned in medieval literature, and it may have an even older tradition among the Sami people, with the oldest findings of bark harvests being around 3000 years old. During the 18th and early 19th centuries, Northern Europe experienced several very bad years of crop failure, particularly during the Little Ice Age of the mid-18th century. The grain harvest was badly affected, and creative solutions to make the flour last longer were introduced. In 1742, samples of "emergency bread" were sent from Kristiansand, Norway, to the Royal Administration in Copenhagen, including bark bread, bread made from grainless husks and bread made from burned bones. During the Napoleonic Wars, moss and lichen were used for human consumption.

Source: Wikipedia